Labour has deferred its decision on whether to expel former London mayor Ken Livingstone for alleged antisemitic remarks as senior party figures broke ranks to claim the shadow cabinet was “sleeping” on the job.

After the final day of his behind-closed doors disciplinary hearing on Friday, the party said it would defer its decision on his future to Tuesday.

Arriving for the hearing on Friday, Livingstone defended his comments again and said he was hopeful that the party’s national constitutional committee would rule in his favour: “I’m always hopeful. It’s pretty fair. The injustice was actually suspending me for something I hadn’t said.”

Livingstone’s comments refer to the Haavara agreement signed by the Nazi government that facilitated the relocation of some Jews to Palestine in 1933, before the Third Reich began its campaign of mass extermination. However, Livingstone’s claim that the agreement had meant Hitler was supportive of a Jewish homeland has been widely disputed by historians.

Meanwhile, Ian Austin, a former Labour minister, accused the front bench of being “pitiful” at opposition research and rebuttal.

Responding to media criticism of the party’s press operation, he said: “We have lots of reasons to be embarrassed, but the press office isn’t one of them... Not the staff’s fault if the shadow cabinet are asleep.”

Ian Austin (@IanAustinMP)

@SamCoatesTimes We've tried! The shadow cabinet are the problem. I once analysed how many questions they'd tabled. Was pitiful.

Several journalists had accused Labour’s press office of being slow to react to breaking news.

In a rare intervention, Labour’s general secretary Iain McNicol also signalled the delays were not the fault of the press office staff, insisting they were “some of the most committed, brightest and best”.

Infighting has broken out between Labour front and backbenchers in recent weeks, with some shadow cabinet ministers furious that their predecessors – who were sacked, resigned or refused to take jobs – are still effectively trying to keep their old portfolios by getting quoted in the media, obtaining urgent questions and pushing for legislative changes.

“The ‘shadow shadow cabinet’ needs to pipe down and let us do our jobs,” one of Jeremy Corbyn’s senior team said.

Tensions are also brewing among London Labour MPs after a recent poll found Corbyn scored negatively among every political or demographic group in the capital, including age, gender, social class, remain or leave voters and in both inner and outer London, regardless of political affiliation. His overall approval rating was -44 in the YouGov research by Queen Mary University London.

Liberal Democrats have doubled their support in the capital since the EU referendum, according to the research, and the party has the potential to gain several seats back from its crippling 2015 election losses, including Hornsey and Wood Green and Bermondsey and Old Southwark.

The negative polls were a stark comparison to the popularity of the Labour mayor in London, Sadiq Khan, who was found to have a strong approval rating of +35, with 58% of those surveyed saying he was doing a good job, compared with 62% who said Corbyn was doing badly. Even among those who voted Labour in 2015, Corbyn’s rating was -35.

One London Labour MP said: “These are terrible numbers again, but especially for a Labour leader who is a London MP. Jeremy should know that when you can’t even win support in London as a London MP, the project has failed. The huge difference in support between him and Labour’s mayor Sadiq Khan speaks volumes.”

Another London Labour MP, with a tight marginal seat, said they were despairing at the poll. “Sadiq is actually making a difference for London, and the leadership are not making any impact at all. It’s just incompetence.”

The MP said the popularity of Khan showed a majority of Londoners still wanted to back a centre-left candidate. “He has to realise that the problem is him, and if he doesn’t go, people will lose their seats and that is doing Labour a disservice.”

On Thursday, Labour’s national constitutional committee heard that Livingstone had brought the party into disrepute by suggesting Hitler had supported Zionism, assertions Livingstone repeated at length to reporters outside the meeting that morning.

Livingstone, a key ally of Corbyn, could add to the party’s internal woes if he brings a judicial review against any decision made by the national constitutional committee on Tuesday.

“The obvious thing would be a judicial review, because that would be heard in public and that would be the best way of clearing the air of these lies and smears,” he told the London Evening Standard. “This isn’t North Korea. We are supposed to be an open democracy.”